15N-studies in severe renal failure

Urea containing heavy nitrogen was given intravenously to two uraemic patients. Essential amino acids were administered daily by mouth or intravenously. Protein from muscle samples and plasma protein was hydrolyzed. 15N-excess in the isolated amino acid nitrogen was determined. 15N was recovered in all the amino acids except in threonine, lysine, and histidine. The results were compared with those from a patient in severe post-traumatic catabolism. In this case, and in a previously studied healthy volunteer, 15N was recovered also in histidine from muscle and plasma protein. This difference in 15N-distribution between the uraemic patients, and the healthy subject and the patient in post-traumatic catabolism, supports the hypothesis that histidine is an amino acid which is essential in severe uraemia.